Seals for a wide variety of uses and purposes have been developed over the years. One of the more effective sealing materials, especially for relatively higher temperature environments, such as in automotive head gaskets where typical elastomers tend to degrade over a period of time, has been silicone rubbers and the like. They are widely used, as by depositing such in printed patterns.
However, there are difficulties in using silicone elastomers in gaskets. These result from their relatively low structural strengths and their low extrusion resistance. As a result, if a silicone seal or bead disposed on a surface is compressed excessively, it may extrude and split, producing leakage paths which result in a loss of its sealing capacity.
In the past, seals of elastomeric materials have been deposited in embossments and the like to confine them under compression. The embossments or other containing configurations generally have been of a volume slightly less than that of the sealing material. Thus, as the sealing material under compression tended to extrude or flow, it would largely be confined by the walls of the embossment or other configuration. Patents showing filled embossments include U.S. Pat. Nos. 3,721,452; 4,397,472; and 4,140,323. German Pat. No. 819,177 and French Pat. No. 1,297,195 are of interest in this regard as well.
However, that mode of preventing destructive extrusion of low extrusion-resistant material beads requires special configurations and does not solve the problem of preventing destructive extrusion of sealing beads which are disposed on the relatively flat surfaces of generally flat gaskets. Thus, in connection with flat gaskets, it has been suggested that hard stops, such as epoxy materials, be applied to the surfaces of gaskets in strategic locations to prevent destructive extrusion of elastomers. U.S. Pat. No. 3,794,333 shows such an approach. However, the utility of that approach is limited to specific types of gaskets and substantially affects the sealing characteristics of the remaining gasket portions.
Thus, improved means for facilitating the use of low extrusion-resistant elastomeric beads is desirable.